Electrode composition for electron-discharge devices



Feb. 11, 1930. s. DUSHMAN 1,747,063

ELECTRODE COMPOSITION FOR ELECTRON DISCHARGE DEVICES Filed July 2, 1923 MQGA/fS/UM OR CALC/UM Inv-ehtor: Saul Bushman,

His Attorney Patented Feb. 11, 1930 SAUL SGHENECTAIDY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A. CORPORATION OF NEW YORK nmac'rnonn comrosrrrou ron Application filed July 2,

The present invention relates to the constitution of cathodes for electrical discharge devices, as for example, radio detectors, rectifiers and the like. I

The object of my invention is to provide a cathode material capable of high electron emission at an operating temperature which is relatively low and which therefore permits of operation of the device by a low heating current capable of being furnished by an ordinary primary battery.

I have found that the elementuranium is capable of a high electron emission at a temperature as low as about 1500 0., and in accordance with my invention an oxide of uranium is incorporated into an electrode which is operated under conditions permitting reduction of at least part of the uranium, where by the electron emissivity of the electrode is very materially improved.

When making an electrode embodying my invention, a finely divided uranium compound is incorporated with the material constituting the main body of the electrode, as distinguished from a surface application. For example, in the manufacture of a tungsten cathode embodying my invention, a suitable non-volatile compound of uranium is mixed with the finely divided metallic tungsten from which cathode filaments are fashioned either in accordance with the Coolidge mechanical working process described in the U. S. Patent 1,082,933 of December 30, 1913, or by squirting of the finely divided material admixed with a suitable binder.

When manufacturing drawn tungsten cathodes about one to two per cent of uranium oxide or other suitable non-volatile compound of. uranium is mixed with the finely divided tungsten metal before it is pressed into slugs preparatory to sintering. In general, as much uranium compound is added as may be tolerated in the tungsten without interfering with the subsequent swaging and drawing in accordance with Coolidge Patent 1,082,933.

In some cases it may be more convenient to form electrodes from a mixture of metal and a uranium compound, by adding a suitable binder in sufiicient quantity to produce a plastic mass and squirting the same into fila- ELECTRON-DISCHARGE DEVICES 1923. Serial No. 648,877.

ments or ribbons. For example, filaments may be made by squirting a mixture comprising by weight about 95 parts tungsten, 5 parts uranium oxide and enough carbonaceous binder to form a mass capable of being squirted, and thereupon baking, treating to remove the binder, and sintering in the usual way.

When filaments made in this way are mounted as cathodes in an electron discharge device, such as shown for example in the drawing, comprising a bulb 1, a cathode 2, an anode 3 and a grid 4, precautions should be taken to thoroughly evacuate the bulb and contained parts, especially to remove water vapor. The electron device is provided as usual with the cathode leads 5, 6, an anode lead 7 and a grid lead 8, all of which are sealed into a stem 9 and connected to terminals (one numbered 10 being shown) sealed into a case 11. However, as these structural features form no essential part of my invention they will not be described in greater detail. Preferably, but not necessarily, a material of low vapor pressure which is highly reactive to water vapor, as for example magnesium or calcium, is introduced into the bulb. In the device shown in the drawing it is present as a film 12 on the bulb wall.

When the evacuation is complete and preferably when the bulb has been scaled the cathode is activated by heating to a temperature of about 2000 to 2500 C. for about a minute and then formed at about 1500 to 1600 C. for a few minutes. Heating to 2000 to 2500 C. results in a reduction of a small part of the uranium oxide to metallic uranium which difi'uses at the forming temperature to he cathode surface where it remains in greater part as an adsorbed film. The temperature of normal operation preferably is materially lower, usually below 1500 C. as at the higher temperatures uranium tends to be vaporized from the incandescent tungsten. At about 1700 C. the evaporation is quite rapid. Cathodes containing uranium oxide after having been activated and formed as above described, when operated at 1425 0., give an electron emission of about 30 milliamperes per sq. cm. of emitting surface, whereas pure tungsten at the same temperature has the extremely low electron emission of about 0.0006 of a milliampere per sq. cm. In general cathodes containing uranium as an ele mentary constituent should be operated at a red heat below bright incandescence. v

Conveniently, but not necessarily, a nonvolatile reducing agent, such as carbon, is in corporated into the cathode in order to assist in reducing the uranium compound particularly when for an reasonwater'vapor is evolved. even thoug in minute quantity during the operation of the device. Carbon may be introduced by heating the filamentv in the presence of the vapor of a carbon compound, as or example, the vapor of anthracene ornaphthalene. The pressure of this vapor should be maintained at a low value and the temperature of the cathode, the

. time of treatment and other conditions should be so regulated as to maintain the carbon content less than about one per cent and preferably as low as about one-half per cent.

Although the manufacture of a tungsten base electrode has been describedfor the purpose of illustrating my invention, I wish it to be understood that the benefits of my invention also may beobtained in the case of electrodes consisting wholly or largely of other metals, as for example, molybderum or nickel.

What I claim as new andflesire to secure by Letters Patent of the United States, is, 1. The process of treating an, electrode containing uranium as a constituent which consists in heating said electrode in non-oxidizing environment to about 2000 to 2500 C. then heating to about 1500 to 1600 C. and finally operating said electrode at a lower temperature.

2. The process of treating an electrode con-- taining uranium in a non-oxidizing environment which consists in heating said electrode to about 2000 to 25009 G. for about one minute,'then heating to about 1500 to 1600 C.

for several minutes, and finally. operating said electrode at a temperature below and adjacent to 1500 C. l

In witness whereof, I have hereunto set my hand this 30th day of June, 1923 I SAUL DUSHMAN.

l memes 

